Lead free soldering quality problems in electronics

Full text: There is a growing interest in lead-free soldering in Europe mainly driven by forthcoming legislation banning the use of lead solders in electronics by July 2006. Currently the most favoured alloys (SnAgCu, SnCuNi, SnCu) to replace tin/lead solders all have 30-400 C higher melting temperature than the traditional Sn63Pb37 eutectic alloy. Therefore in general lead-free solder pastes recommend a peak temperature range 30-400 C higher as compared to Sn/Pb solder. Due to the higher reflow peak temperature the use of some materials, components, technological processes and equipment may not be feasible for Pb-free assembly. The use of new materials and higher reflow temperatures in Pb-free soldering processes causes various problems on solder joint quality and reliability. One of them is wetting behaviour. The surface tension of the lead free alloys is significantly higher than Sn/Pb therefore they wet more slowly than Sn/Pb alloys at any temperature. Critical problems, especially in the case of wave soldering, are associated with fillet lifting due to the larger temperature change during the process. Additional problem is the higher cost of lead-free soldering materials. The use of pure tin finishes as an economical lead-free plating option has the threat of failure due to tin whiskering. Methods for solder joint quality control should be modified including standard criteria formulation for visual and X-ray inspection methods as well as reliability tests should be improved